Building the Tiny Giant amp

[myramyd]

The heat sink of the LM338T is not showing connected to ground but the TD7240A heat sink is (it was before this happened also). I have the spacers installed on both.

J

[Taylor]

Hmm. Nothing springs to mind - I guess I'd look physically around the board to see if there's anything shorting these parts to ground. But you've probably tried that.

[myramyd]

Yeah, nothing really looks like it--although I  haven't pulled it out to look on the bottom of the board yet.

The one question I have--does the circuit have any kind of polarity protection? If you recall, I'm the one who first wired up the power backwards and blew out the LM338 chip. I replaced that chip and fixed the polarity and it has been working fine since then. I'm just wondering if I could have damaged something else back at the beginning and it just finally went? That's the only other thing I can think of.

J

[Taylor]

There's no polarity protection on the board. I would be surprised if damage like that would be sustained but take such a long time to have any impact. I'd suggest taking a look under the board - it's quite possible that a pointy solder joint could poke through whatever you're using to isolate the board from the box, or something similar.

[waltk]

The heat sink of the LM338T is not showing connected to ground but the TD7240A heat sink is (it was before this happened also). I have the spacers installed on both.

The heatsink tab on the TDA7240 is internally connected to pin 4 (ground) , so you don't need to worry about that.  Pins 5 and 7, however, should only go to your output jack - and neither should be grounded.

According to the datasheet...
"Reliable operation is guaranteed by a comprehensive
array of on-chip protection features. These include
protection against AC and DC output short
circuits (to ground and across the load), load dump
transients, and junction overtemperature. Additionally,
the TDA7240A protects the loudspeaker when
one output is short-circuited to ground."

So temporary shorts of this kind shouldn't cause any permanent damage.

The heatsink tab on the LM338 is internally connected to Vout, and should never be allowed to touch ground.

While you're poking around the board, you should probably verify that all the external connections are still intact (power in, speaker out, etc.).

[arma61]

Sorry myramyd and all you guys to interrupt this troubleshooting... but it's just arrived!



The board is designed to have "on board"
-a power reguator to get the 9V
-an overdrive, it's the Easy Drive
-the wellknown One Chip Chorus, layout blatantly copied from Earthscum's layout 
-a Cabinet simulator, it's the Condor Cab Sim from ROG, on my own layout heavily based on Gringo's
-a relais switching to switch only the OD and the Chorus, the CabSim has its own DPDT on the front Panel

The big pad u c on the left is there because at the beginning I wanted to include the TGA on the board, but I did't dare to!! Taylor kit is sooo good!!!, so I leave the pad (and the other small one, to save etchant!! )

I'm just populating it right now!! hopefully everything will be ok.

Ciao
Armando

[Taylor]

Looks great Armando.

[bcalder]

Hi all, it's about time for a newbie question. 

In place of the SPST toggle, I want to use an illuminated pushbutton similar to http://www.velleman.eu/products/view/?id=376866

My questions:
1) For this one in particular, I would wire it as NO, correct?
2) How do I feed current to the LED? I'll be using the extra 11.x volt output to power a preamp - can I still take it from there?
3) What size of CLR would I use in any case, the same as for a stompbox?

Many thanks in advance!!

[Taylor]

Your link won't work for me - it just sends me to the home page - and I couldn't find it searching. Could you post the item number?

[PRR]

> sends me to the home page

Actually to the Pick-A-Country page, right? And Velleman does not offer all products to all countries.

Try this:
http://www.velleman.eu/products/view/?country=nl&lang=en&id=376866

FLAT STAINLESS STEEL PUSH BUTTON SPST 1NO 1NC - ORANGE RING

Has an awful lot of pins:

SPDT 1NO 1NC
colour: orange
power supply LED ring: 12VDC
type: (on)-off
connections:
NC (normal closed): 1-2
NO (normal open): 3-4

[bcalder]

Sorry for posting that one - my question is simply how to hook up an on/off SPST with a built-in LED.

Here's a couple of simpler ones that would make me just as happy :-) If you have trouble with the link, I picked Spain & English language on the home page.

This product ID is R1945A:
http://www.velleman.eu/products/view/?id=339466

This one is R1399B - same idea, I think:
http://www.velleman.eu/products/view/?id=385530

[bcalder]

Hm, maybe I see the answer ... In looking at what PRR posted, it LOOKS like all I have to do is feed the switch 12V, figure out which lugs are the NO ones,  & all will be well. Can I just "split" the 11.3V output I will use to feed the preamp and send 11.3V to the pre & 11.3V to the LED switch, or does something have to be done to it first?

[potul]

Hi Guys,

I received my Kit from MusicPCB some weeks ago and I'm now buying the rest of components to put an amp together. I have a doubt regarding the volume pot.... Do I need a log or linear one? Schematics says "A", but you know... this means different things in Europe than in US... I assume it's a log ("Audio") one, but I'm not sure...

REgards,

Mat

[Taylor]

Ah yes, I forgot about the Europe/US taper thing. I'm in the US, so I'm using the US terms. A is log (audio), B is linear.

My mnemonic is "A for audio, Linear B". Linear B being the famous ancient Greek script, of course. 

[potul]

Great, thanks for the clarification!

[Flemming]

New member, new builder, new in general I did my best to chew through the full length of the thread, but i'll definitely still have tons of stoopid questions!

First of all, thanks to Taylor for making this project officially available. I received the envelope full of goodness yesterday. Parts of nice quality, sexy PCB. And I'll get a suitable laptop PSU on Monday - really looking forward to test this little monster. I foresee it putting my LM386-based Ruby amp to shame It took me approximately 30mins to assemble (including a bit of time 'identifying' the resistors, using my own homebuilt 'resistor colorcode calculator'). Second of all, I just love how all these old laptop PSUs are being 'recycled' in such a meaningful way. Seriously, call me a hippie or whatever It really warms my heart to experience environmental responsibility in the guitar DIY scene!

- In reply #218 haroldjenkins offers a nice solution to incorporate an output for headphone. But won't it sound harsh without some cab simulation? Has anyone tried this out one way or another?

- I dream of stuffing some kind of tube-based preamp into the box also. I have the PCB for a SLO clone, but also the 'Pepper Shredder' looks good (http://www.tube-town.net/diy/lov/lov02-peppershredder-eng.html). Coupling together such two circuits, should I be aware of stuff like impedance or any-other-kind-of-electrical-expression-that-i-don't-know-anything-about which might impact on the sound in an undesirable manner??!

Anyways, I promise to do my best And I'll post some pictures as my build (hopefully) carries on.

[Flemming]

I got hold of this IBM PSU today

http://imagehost.vendio.com/a/35097889/aview/IBM_Adapter_12J1443.JPG

It says 16V 2.2A, so I hope it'll do the job nicely... I really itch to test this out, but since i have no heatsink attached to the PCB yet, i'm afraid to fry my Tiny Giant :S

- Would my newfound PSU be able to feed my TG properly? I read that it needs an amp rating swinging from 1A to 5A throughout the thread here

- Could i be so cheeky to turn on my TG and test it for sound, rapidly like 30secs or something without chance of frying the little baby?

Cheers,
Flemming

[Taylor]

That supply should work.

Re heat sinks, I can't recommend that you do that since you might wreck it and then blame me.  I would just try to screw the chips to any piece of metal on which you can get your hands.

[musicisphysics]

Taylor,

I already have a very clean 10VDC supply (40,000 uF worth of filtering), so could I just bypass the LM338T and use unregulated power without dire consequence

[Taylor]

You can do that and I foresee no dire consequences, but you will get lower power output with only 10v.